Asymmetrical waveguide



Jan. 17, 1967 e. SCHICKLE ETAL 3,299,374

ASYMMETRICAL WAVEGUIDE Filed April 5, 1965 I 4 Sheets-Sheet 1 7.4 ELLIPTICAL -cRoss SECTION n. I DEVICE OF FIG. 2

Fig. 1

Gerhard Schickle Wolfgang Krcmk 8 Erich Schlitflbffel ATTORNEYS mvENToRs G.SCHICKLE ETAL ASYMMETRICAL WAVEGUIDE Filed April 5, 1965 4 Sheets-Sheet 2 INVENTORS Gerhard Schickle Wolfgang Krcmk 8 Erich Schiittlbffel ATTORNEYS wfamgw G. SCHICKLE ETAL siMMETRIcAL WAVEGUIDE Jan. 17,1967

4 Sheets-Sheet 5 Filed April 5, 1965 Fig.6

INVENTORS Gerhard Schickle Wolfgang Krunka Erich Schiifllfiffel WW; 7%

ATTORNEYS il 67 a. SCHICKLE ETAL I I I ASYMMETRICAL WAVEGUIDE Filed April 5,1965 4 Sheets-Sheet 4 Fig. :0

' INVENTORS Gerhard Schickle Wolfgang Krunk 8\ Erich Schiittlfiffel M W 4 A ORNEYS United States Patent 3,299,374 ASYMMETRICAL WAVEGUIDE Gerhard Schiekle, Wolfgang Krank, and Erich Schiittliiffel, Backnang, Wurttemherg, Germany, assignors to Telefunken Patentverwertungs-G.in.b.H., Ulm (Danuhe), Germany Filed Apr. 5, 1965, Ser. No. 445,506 Claims priority, application Germany, Apr. 4, 1964, T 25,956; May 8, 1964, T 26,155; Dec. 12, 1964, T 27 ,605

21 Claims. (Cl. 333-95) The present invention relates generally to the microwave art and, more particularly, to a flexible waveguide for the correct transmission of a particular Wave type, preferably a linearly polarized electromagnetic wave, in which the two axes of the cross-sectional plane are of different length.

It is known to use waveguides with different crosssectional shapes for the transmission of a high frequency electromagnetic wave. These waveguides normally have a round or rectangular cross section.

Recently, flexible waveguides became known having cross sections which are elliptical. The flexibility is in this case provided by a preferably spiral-shaped cor1rugation of the waveguide sheath. In flexible waveguides there is always the risk that undesired forms of oscillation which move along the waveguide occur, due to the corrugations. This causes a considerable distortion of the electrical behavior of the waveguide. The above-mentioned elliptical corrugated waveguide does not have this disadvantage, but it has been found that the chosen form of the cross section is not sufiicient or does not represent an optimum for all purposes of application. This is due to the fact that there was a need to compromise between the desired electrical and mechanical qualities. The conventional crosssectional shapes of non-flexible waveguides do not provide optimum solutions with respect to present electrical and mechanical requirements, and such as rigidity and manufacturing requirements.

With this in mind, it is an object of the invention to provide a flexible waveguide which avoids the above disadvantages of waveguides having conventional shapes.

Another object is to provide a waveguide having such electrical characteristics that it will provide correct transmission of a particular wave type, preferably linearly polarized waves, and an optimum solution is provided regarding relative frequency, bandwidth and/or attenuation without presenting mechanical disadvantages.

A further object is to provide a waveguide of the character described which can be manufactured as easily as a round or rectangular waveguide.

These objects and others ancillary thereto are accomplished in accordance with preferred embodiments of the invention wherein a flexible waveguide for the correct transmission of a particular wave type, preferably a linearly polarized electromagnetic wave, is provided, in which the two axes of the cross-sectional plane are perpendicular to each other and have different lengths. The waveguide cross section is asymmetric at least relative to one axis and the edges of the cross section do not have abrupt changes of direction.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a graph plotting relationships indicative of waveguide cross section'axes ratio to relative bandwidth.

FIGURE 2 is a schematic sectional view of one embodiment of the waveguide of the present invention.

"ice

FIGURE 3 is a schematic sectional view of another embodiment FIGURE 4 is a schematic sectional view of a further embodiment.

FIGURE 5 is a schematic sectional view of one arrangement for loading a waveguide of the present invention.

FIGURE 6 is a schematic sectional view of another arrangement for loading a waveguide.

FIGURE 7 is a schematic sectional View of a arrangement for loading a waveguide.

FIGURE 8 is a schematic sectional view of a waveguide arrangement using two asymmetric waveguides.

FIGURE 9 shows a schematic sectional view of a waveguide arrangement using two asymmetric waveguides for different frequency ranges.

FIGURE 10 is a schematic longitudinal section of a waveguide loaded at periodic distances with dielectric material.

With more particular reference to the drawings, it should be noted that it is known that the relative frequency bandwidth, which can be transmitted in a rectangular waveguide, is determined by the ratio of the axes of the waveguide. This relationship is schematically rep-resented in FIGURE 1, whereby the relationship f /f is plotted against the axes ratio b/a, where further f is the limit frequency of the first occurring higher type of wave of the particular waveguide cross section (for example. in a rectangular waveguide with a side ratio of 2:1 the H -wave),

1 2 is the limit frequency of the useful wave.

a is the major axis of the cross section, and

b is the minor axis of the cross section.

The curve in FIGURE 1 shows the relationship of the relative frequency bandwidth with respect to the axis ratio for a rectangular waveguide. For a round waveguide this curve coincides with point 1,0 of the horizontal axis because in such a waveguide the waves that are polarized perpendicularly to each other can be transmitted at the same time and according to the definition, only one wave is to be transmitted.

The curve of the relative frequency bandwidths for a conventional waveguide with an elliptical cross section is represented in FIGURE 1 by a dotted line.

The waveguide of the present inventio-nis designed in such a way that its cross section is asymmetric, at least relative to one axis and the edges of the cross section are free of abrupt changes of direction. The transitions of the different parts of the waveguides edge in the cross sect-ion are rounded off.

The asymmetric form of the wave uide cross section is preferably made relative to the major axis. portant that the edges be even, i.e., that they do not have abrupt changes of direction. So, it is possible that the edges be substantially formed by circular arcs or circular arc-like lines. It is especially advantageous in this case to design the edges in such a way that the center of one of the two different circular arcs, or circular arc-like lines is outside of the cross section. These portions of the edges have to be different from each other, in order to obtain the desired asymmetry of the cross section relative to one axis.

FIGURE 2 shows the cross section of a waveguide designed according to the invention. The two axes a and b which are perpendicular to each other have different lengths. In the cross section form shown, an asymmetry relative to the major axis a is provided. Due to this form of waveguide cross section a considerable decrease of the attenuation is obtained, compared to that of the rectangular cross section, and only one wave type can be transmitted. One can, consequently, vary the It is im-' electrical characteristics with respect to the attenuation of the transmitted wave according to the bandwidth within a wide range by selecting suitable radii of curvature. In FIGURE 1, the behavior of such a waveguide is represented by a dash-dot curve.

FIGURE 4 shows a waveguide which is suitable dimensioned in such a manner that the following relationships are provided:

where r, is the radius of the circular arc-like part of the edges which is about parallel to the major axis, r are the radii of the circular arc-like edges that are symmetrical with respect to the minor axis, is the minor axis of the cross section, and D is the major axis of the cross section.

These experimentally found relationships give a waveguide flexible enough for all purposes which has very good behavior with reference to transmitted relative frequence bandwidth and attenuation.

With'reference to FIGURE 4, it should be noted that the preferred cross section of the invention is drawn in heavy lines in FIGURE 4. Its edges comprise circular arc-like portions whereby the cross section itself is substantially determined by the minor axis d and the major axis D. The cross section is flattened on one side and the flattening is parallel to the major axis D and is preferably linear. On the opposite side, the edges are formed by a circular arc-like portion of radius 1- The two circular aro-like edges which are symmetrical with respect to the minor axis d have a radius of curvature r When providing the waveguide with dimensions, it was taken into consideration that while preserving the desired electrical characteristics of such a Waveguide cross section, it should be capable of being manufactured in a simple way by deforming a round waveguide. The cross section has a shape which makes it possible that the waveguide is easily flexible. The mentioned ratio r /a' is preferabiy 0.22 arrd the ratio r /D about 0.57.

If in FIGURE 4 the flattened portion of the edges, which is represented by a straight line, is replaced by a circular arc-like portion, it is suitable to choose the radius R of this part to be considerably larger than the radius r of the opposite portion of the edges. In general, the center point of the radius 1', then is placed inside the edges of the cross section, as shown in this embodiment.

With either type of construction and with all the embodiments shown in the drawings the periphery of the cross section all along its length has a curvature which is free of changes in sign. Thus, while the curvature may be zero (0), e.g., when the periphery includes a straight line, it does not change sign. This means that when following the periphery in a particular direction the curve will always be in one direction, e.g., to the left but will never be in the other direction (in the example, to the right) although there can be no curve (as when it is linear). Thus, the waveguides of the present invention can include a cross section periphery which is convex and possibly also, a straight line.

The ratio d/D of the two diameters of the cross section is substantially between 0.3 and 0.9 depending on the required frequency bandwidth. If optimum attenuation is required, the ratio must be as close to 0.9 as possible.

According to a further feature of the invention, the edges of the waveguide cross section can be formed by elliptical or elliptical-like lines or by haphazardly curved lines. In another embodiment of the invention, as shown in FIGURE 3, the cross section of the waveguide was flattened asymmetrically to one axis, so that a portion of the edges is a straight line. In the cross section shown in FIGURE 3, the linear portion of the edges is parallel to the major axis a of the cross section. The behavior of such a waveguide with respect to the transmitting bandwidth is represented by the dashed curve in FIGURE 1. It can be seen that this waveguide has the largest relative frequency bandwidth.

For many purposes of application (for example, mobile stations) waveguides having great flexibility are needed. For such purposes a flexible waveguide constructed according to the invention is especially advantageous. The required flexibility can, for example, be obtained by using a corrugated tube as a waveguide sheath, which preferably has a longitudinal weld seam and has a spirally-formed corrugation. The production cost of such a ength of waveguide is considerably lower than that of a rigid waveguide, because it can be produced continuously and in any desired length.

Furthermore, it is possible to equip at least a portion of the waveguide interior wall with dielectric material. In one embodiment, the dielectric material is installed, in at least one of the two waveguide wall portions which are opposite, or extend generally in the same direction as, the major axis. The dielectric material functions as a load on the waveguide, which can be a dielectric web within the waveguide and which runs parallel to the longitudinal axis of the waveguide. It is, furthermore, possible to use two diametrically opposite straps.

According to another embodiment, the dielectric material can be installed in the waveguide, preferably at periodic distances.

Since the waveguide is designed to be flexible, the dielectric load is applied in such a way that the flexibility is not influenced disadvantageously, and this, for example, can be provided by using a flexible and preferably foamed dielectric material. Flexible waveguides are mostly designed as corrugated tube waveguides, so that it is possible to have the dielectric material extend, at least partially, into the grooves of the corrugation.

Such waveguides are mostly produced by bending a simple metal band into a round tube, welding it, and then providing it with the desired corrugation. It is therefore, preferable to apply the dielectric material to the flat metal band, which is used for manufacturing the waveguide, so that there can be continuous production. However, if the dielectric load is only installed after the waveguide is manufactured, it is most advantageous to install the dielectric material in the form of one or several straps or webs which run parallel to the longitudinal axis of the waveguide, on the inner wall of the waveguide.

The advantage of a waveguide constructed according to the present invention is, among other things, that by changing the dielectric load at the ends a favorable connection of the required contact elements or terminals can be provided. A waveguide that is so loaded also functions as a so-called ridged waveguide, i.e., its dimensions can be decreased or when usingthe same dimensions a larger bandwidth and higher critical frequency is obtained. By choosing particular dielectric materials it also is possible to decrease the losses to a minimum. For the suppression of undesired wave types at certain places in the waveguide dielectric material can be used for attenuating these wave types. The dielectric load also makes it possible to choose the cross section of the waveguide in such a way, with a particular selection of its form and/or dielectric constant, that the highest possible flexibility is obtained, because the dielectric material has the same effect as flattening a waveguide that has a round cross section. The closer one comes to the round cross section, the greater is the flexibility.

In FIGURES 5 through 7 three embodiments for loading a waveguide 1 dielectrically, are shown. In the embodiment in FIGURE 5, a dielectric web 4 is provided, which is attached to the inside of the flattened portion of the waveguide wall.

Furthermore, as shown in FIGURE 6, it is possible to make the dielectric webbing 5 so large that it covers the entire flattened side of the waveguide.

In FIGURE 7 two webs 6 and 7, made of dielectric material are provided symmetrically with respect to the minor axis of the waveguide, and the web applied on the flattened side of the waveguide, is thicker than the other.

The manufacture of a waveguide having a cross section in accordance with the invention can be made in an inexpensive manner by taking a round, longitudinally welded metal tube and providing it with a corresponding co-rrugation. Then, it is deformed continuously until the desired cross section is obtained.

A radio installation often has to transmit two waves to an antenna array at the same time but independent of each other. This is, for example the case if two polarizations have to be transmitted over one antenna or if the energy derived from two antennas has to be fed into two apparatus inputs independently of each other.

If, according to a further characteristic of the present invention, two waveguides are flattened asymmetrically with respect to the major axis a and arranged in such a way that their flat wall surfaces are adjacent and their axes are parallel to each other, and preferably if they are connected to a unit by a dielectric coating, a transmission guide is obtained, that can be mounted easily, has optimum bandwidths, and at the same time allows the transmission of two waves.

FIGURE 8 shows a waveguide arrangement of two asymmetric waveguides 8 and 9, which serves for the simultaneous transmission of two electromagnetic waves, without mutual interference. The two flat sides of the waveguides are adjacent and their axes are parallel and they are joined into a unit by a dielectric protection coating 3. If the waveguide arrangement shown in FIG- URE 8 is made of flexible corrugated waveguides an easily mountable waveguide is provided for the transmission of two electromagnetic waves. It is also inexpensive to make and, at the same time, provide optimum transmission with respect to the relative frequency bandwidth, due to the selected cross section of the waveguide part 8 and/ or 9, whereby the relative center frequencies, of the individual waveguide, as well as their relative bandwidth can be different.

In FIGURE 9 there is shown a waveguide arrangement of two asymmetric waveguides 10 and 12 with their dielectric coating 11. These waveguides are dimensioned for different vfrequency ranges.

FIGURE 10 shows a longitudinal section of a waveguide 13 which is loaded with a dielectric material 14 that is arranged at periodic distances. The dielectric material extends into the grooves 15 of the spirally corrugated waveguide. Preferably the dielectric material is glued on the corrugated tube.

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

What is claimed is:

1. A flexible waveguide device for the correct transmission of a particular type wave and preferably a linearly polarized electromagnetic wave, comprising a waveguide in which the two axes of the cross sectional plane which are perpendicular to each other are of difi'erent length, the cross section of the waveguide being asymmetrical relative to at least one axis, and the edges of the cross section being smooth and free of corners and the periphery of the cross section having everywhere a curvature which is free of changes in sign.

2. A flexible waveguide device, comprising a waveguide having a cross sectional plane in which the two axes at a right angle to each other are of different length, the cross section of the waveguide being asymmetrical relative to at least one axis and the edges of the cross section being free of abrupt changes of direction and the periphery of the cross section having everywhere a curvature which is free of changes in sign.

3. A device as defined in claim 2 wherein the cross section is asymmetric relative to the major axis.

4. A device as defined in claim 2 wherein the edges of the cross section are mainly of circular arc-like lines.

5. A device as defined in claim 4 wherein the center point of one of the two different circular arcs is outside the edges of the cross section.

6. A device as defined in claim 5 having the following relationships:

where r is the radius of the circular arc-like portion of the edges which is substantially parallel to the major axis, r; are the radii of the circular arc-like portions which are symmetrically disposed with respect to the minor axis, d is the minor axis of the cross section, and D is the major axis of the cross section.

7. A device as defined in claim 6 wherein the ratio 1' d is substantially 0.22.

8. A device as defined in claim 6 wherein r /D is substantially 0.57.

9. A device as defined in claim 6 wherein there is a generally flattened portion formed by a circular arc-like line of radius R and wherein 10. A device as defined in claim 2 wherein the edges are mainly formed of elliptical-like lines.

11. A device as defined in claim 2 wherein at least one portion of the edges is linear.

12. A device as defined in claim 11 wherein said linear portion is parallel to the major axis.

13. A flexible waveguide device, comprising a waveguide having a cross sectional plane in which the two axes at a right angle to each other are of different length, the cross section of the waveguide being asymmetrical relative to at least one axis, the edges of the cross section being free of abrupt changes of direction, and dielectric material arranged at least partly on the inner wall of the waveguide.

14. A device as defined in claim 13 wherein the dielectric material is applied to one of the wall portions of the waveguide opposite the major axis.

15. A device as defined in claim 14 wherein the dielectric material is in the form of a continuous web which extends parallel to the longitudinal axis of the waveguide.

16. A device as defined in claim 15 wherein two webs are provided opposite each other.

17. A device as defined in claim 14 wherein the dielectric material is arranged at periodic distances.

18. A device as defined in claim 13 wherein the waveguide is a corrugated tube having a longitudinally extending weld seam and spirally arranged corrugations.

19. A device as defined in claim 18 wherein the dielectric material extends at least partly into the grooves of the corrugation.

20. A waveguide device, comprising, in combination:

(a) two waveguides, each having a cross-sectional plane in which the two axes at a right angle to each 7 other are of different length, the cross section of the References Cited by the Examiner I Waveguide being asymmetrical relative to at least Montgomery, G et 211: Principles of Microwave 3 3X15 h edges of the cross a Circuits, Radiation Laboratory Series, vol. 8, 1948. linear portion parallel to the ma or axis and bemg free of abrupt changes of direction, said waveguides 5 References Cited by the Applicant having their linear portions adjacent one another and their axes parallel to each other; and FOREIGN PATENTS (b) a dielectric covering connecting said Waveguides 425,104 9/1947 Y- to provide a unit. 21. A device as defined in claim 20 wherein the two 10 HERMAN KARL SAALBACH P r 1mm) Exammeh Waveguides are arranged for difierent frequency ranges. L, ALLAI-IUT, Assistant Examiner. 

1. A FLEXIBLE WAVEGUIDE DEVICE FOR THE CORRECT TRANSMISSION OF A PARTICULAR TYPE WAVE AND PREFERABLY A LINEARLY POLARIZED ELECTROMAGNETIC WAVE, COMPRISING A WAVEGUIDE IN WHICH THE TWO AXES OF THE CROSS SECTIONAL PLANE WHICH ARE PERPENDICULAR TO EACH OTHER ARE OF DIFFERENT LENGTH, THE CROSS SECTION OF THE WAVEGUARD BEING ASYMMETRICAL RELATIVE TO AT LEAST ONE AXIS, AND THE EDGES OF THE CROSS SECTION BEING SMOOTH AND FREE OF CORNERS AND THE PERIPHERY OF THE CROSS SECTION HAVING EVERYWHERE A CURVATURE WHICH IS FREE OF CHANGES IN SIGN. 